The invention lies in the field of electronics. The invention relates to a method for controlling a capacitive actuator, in particular a piezoelectric actuator for a fuel injection valve, and an apparatus for carrying out the method.
A method and a configuration for carrying out a related method are described in German Published, Non-Prosecuted Patent Application DE 196 44 521 A1, corresponding to U.S. Application No. 09/299,367, filed Apr. 26, 1999. In that method, a predetermined energy is fed to a capacitive actuator. The feeding takes place by defined charge transfer of a charging capacitor to the actuator, the charging capacitor being discharged from an initial voltage value to a final voltage value. Alternatively, the energy applied to the actuator is determined by measuring the values of the current and voltage flowing or present at the actuator.
It is accordingly an object of the invention to provide a method and apparatus for controlling a capacitive actuator that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that controls a capacitive actuator to diagnose the functional state of an actuator or a fuel injection valve.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for controlling a capacitive actuator, including the steps of determining an energy applied to an actuator, measuring an actuator voltage present at the actuator, and inferring a functional state of the actuator by using the energy and the actuator voltage.
One advantage of the invention is that a functional state of an actuator is quickly and reliably detected in a simple way. The method according to the invention also enables distinguishing between different fault types, for example, a fuel injection valve that no longer opens or closes.
In accordance with another mode of the invention, the inferring step is performed by inferring a functional state of the actuator by using the energy and a deviation of the actuator voltage from at least one reference value.
The invention is based on the idea of inferring the actuator deflection, and, consequently, the functional state of the actuator or the fuel injection valve, from an energy value applied to the actuator and an actuator voltage measured at the actuator.
In accordance with a further mode of the invention, there is provided the steps of inferring a correct functional state of the actuator when an actuator voltage lies between a lower reference value and an upper reference value, inferring a first type of fault when an actuator voltage falls below the lower reference value, and inferring a second type of fault when the actuator voltage exceeds the upper reference value.
In accordance with an added mode of the invention, there is provided the steps of determining a plurality of values for the energy and the associated actuator voltage and inferring a functional state of the actuator by using the plurality of values.
In accordance with an additional mode of the invention, there is provided the step of changing at least one reference value in dependence upon an actuator temperature.
In accordance with yet another mode of the invention, there is provided the steps of sensing operating points of the actuator that are associated with a type of fault, and determining at least one reference value by using the operating points.
In accordance with yet a further mode of the invention, the inferring step is performed by inferring a functional state of the actuator by using at least one measured variable.
In accordance with yet an added mode of the invention, the at least one measured variable is an intrinsic noise of an internal combustion engine.
In accordance with yet an additional mode of the invention, there is provided the step of inferring an actuator stroke by using the energy and the actuator voltage.
With the objects of the invention in view, there is also provided a method for controlling a capacitive actuator, including the steps of determining an energy applied to an actuator, measuring an actuator voltage present at the actuator, and inferring an actuator stroke by using the energy and the actuator voltage.
With the objects of the invention in view, there is further provided a method for controlling a piezoelectric actuator for a fuel injection valve of an internal combustion engine, including the steps of determining an energy applied to an actuator, measuring an actuator voltage present at the actuator, and inferring a functional state of the actuator by using the energy and the actuator voltage.
With the objects of the invention in view, there is additionally provided a circuit for controlling a capacitive actuator, the circuit including a driving circuit having a main switch, a charging capacitor connected to an energy source through the main switch, a first series circuit parallel to the charging capacitor, the first series circuit including an oscillating coil connected to the main switch, an auxiliary switch, and a second series circuit parallel to the auxiliary switch, the second series circuit having a parallel circuit including a discharging switch and a charging switch, and another circuit including a diode to be connected in parallel to the actuator conducting in a direction to ground, and a control device for driving the driving circuit, the control device receiving input signals and having a program and a family of characteristics with actuator characteristics defining characteristic curves, reference values, and correction factors compensating for temperature and for losses of the driving circuit, the control device controlling the main switch, the auxiliary switch, the charging switch, and the discharging switch with the program dependent upon the input signals and upon the characteristic curves of the family of characteristics, the input signals including at least one of the actuator voltage, the actuator temperature, at least one measured variable, and a driving signal.
In accordance with a concomitant feature of the invention, the circuit for controlling a capacitive actuator controls a piezoelectric actuator for a fuel injection valve of an internal combustion engine.
Other modes and features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and apparatus for controlling a capacitive actuator, it is nevertheless not intended to be limited to the details shown, because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.